1. Field
Many aspects of this disclosure relate to a deflectable catheter assembly and methods of making and using such deflectable catheter assembly. For example, the catheter assembly of an exemplary embodiment includes a deflectable distal section, a non-deflectable section, a proximal catheter handle, and a tool such as a needle, a therapeutic device, and a diagnostic device.
2. Discussion of Related Art
Steerable catheters have been commonly used in applications such as mapping (e.g., cardiac mapping), drug delivery (e.g., intramyocardial drug delivery), and ablation, (e.g., arrhythmia ablation).
A steerable catheter has a deflectable flexible distal section and a stiffer proximal torqueable shaft. The steerable function is accomplished by three modes of actions: 1) translational catheter movement along the shaft direction, 2) deflection of the distal deflectable section, and 3) turning of the catheter shaft to direct the deflection toward the target therapy site. A tendon wire is included to control the deflection of the distal section. This tendon wire is located inside of a sheath running along and within the catheter shaft with its distal end attached near the distal tip of the catheter. A pulling mechanism is included within the proximal catheter handle, which is coupled to the proximal end of the catheter shaft. The pulling mechanism controls the tendon wire to deflect the distal section of the catheter shaft. Radially, the tendon wire is located off-center of the catheter shaft center to create a moment toward the intended deflection side in the catheter distal deflectable section. When the tendon wire is pulled, the catheter deflects toward the radial direction to which the tendon wire is located. The deflection section is typically made to be much more flexible than the rest of the catheter shaft. When the tendon wire is pulled in tension, the catheter shaft wants to “curl up.” The distal section is the most flexible section of the catheter shaft and thus it deflects when the tendon wire is pulled. To direct the deflected section toward the target site, an operator turns the catheter shaft on the proximal end. The deflection section responds to the torque in a fashion that is governed by the way the catheter is constructed.
Depending on the therapeutic use of the catheter, a therapeutic tool, such as a needle, may run in parallel to the tendon wire within the catheter shaft.
One problem commonly occurring in the working of this kind of catheter is that the catheter whips when rotated from the proximal end of the shaft. Whipping is caused by the resistance of the catheter to turn away from its preferred orientation, which is generated by unbalanced stiffness over the cross-section of the catheter shaft. This whipping problem gets further magnified when the catheter distal section is deflected and/or when the catheter is resident in tortuous vasculature.
For example, in a catheter that has a needle running through a central lumen within the catheter shaft, the tendon is placed off-center. As can be imagined, the cross-section of the catheter shaft now has an unbalanced radial cross-section created by the tendon wire in its lumen construction. When the catheter shaft is placed over a curved anatomy section, such as the aortic arch, the stiffer tendon wire section has a tendency to stabilize itself toward the outside of the curve (resulting in the lowest energy state). If one tries to rotate the catheter shaft out of this preferred orientation, with the stiff section turning to the inside of the bending curve, the catheter shaft will resist this turning, requiring an applied torque in excess of that required if the catheter shaft had a balanced stiffness and resulting in an increased amount of shaft torsional distortion (wind-up) and accompanying stored torque in the catheter shaft. As one continues to rotate the catheter shaft just past the point with the stiff section directly at the inside of the bending curve, the resistance to turning is suddenly reduced, because the catheter shaft is returning toward its preferred orientation. The stored torque of the catheter shaft now exceeds that required for turning and the catheter shaft rapidly unwinds its wind-up until they are in balance. From the viewpoint of an operator who is turning the proximal end of the catheter shaft at a relatively constant rate, the distal end of the catheter shaft appears to slowly rotate away from its preferred orientation, then when it gets to 180-degree away from its preferred orientation, it suddenly and uncontrollably speeds up and rotates past an adjacent arc of rotation. This sudden and uncontrollable rotation is referred to as whipping. To attain an orientation in the adjacent arc that the distal end of the catheter shaft rotated past, the proximal end of the catheter shaft is required to be rotated back in the opposite direction. In many cases, it is impossible to get the distal end of the catheter shaft to maintain an orientation in the vicinity of 180-degrees away from its preferred orientation with the rotation of the proximal end of the catheter shaft even if the proximal end of the catheter shaft is rotated in the opposite direction. For an operator that only has control of the catheter's proximal end, whipping makes accurate control of the orientation of the catheter's distal end difficult, time consuming, and often very frustrating.
The whipping problem becomes more pronounced when the tendon is pulled to deflect the distal section. Pulling of the tendon creates compression (“curling up”) in the radial side where the tendon locates. Therefore, this compressed side has a preference to reside on the inside of the bending curve. The turning of the catheter shaft now has to work against not just the preferred orientation due to unbalanced stiffness but also against the compression load occurring preferentially on one side of the catheter shaft.